Water destructible electric match



FIG. 2

W. D. TREVORROW Filed March 24, 1967 WATER DESTRUCTIBLE ELECTRIC MATCH Dec. 10, 1968 United States Patent O 3,415,189 WATER DESTRUCTIBLE ELECTRIC MATCH William D. Trevorrow, Tamaqua, Pa., assigner to Atlas Chemical Industries, Inc., Wilmington, Del., a corporation of Delaware Filed Mar. 24, 1967, Ser. No. 625,736 12 Claims. (Cl. 102-28) ABSTRACT F THE DISCLOSURE In the art of electric matches and electric explosion initiators, a water destructible electric match lhaving a coating or film generally characterized as a water dispersible polymeric material which renders the match inelective in the event of misre and which is particularly useful for olfshore seismographic prospecting.

The present invention relates to a water destructible electric match and to electric explosion initiators containing same. More particularly, the present invention relates to a water destructible electric match having a coating of a water dispersible polymeric material and being useful for detonators employed in seismographic exploration.

Electric explosion initiators usually include a metallic shell encasing an explosive charge and an electric match positioned in ring relationship with the charge. Customarily an electric match includes two elongated electrical terminals separated by a non-conducting insulating material. The electrical terminals are connected at one `end by means of a bridge wire about which is formed a match head of an ignition composition. The ignition composition is in contact with the bridge wire which is heated by an electric current to a temperature at which the ignition composition fires and the initiator thus explodes.

Typically, the ignition composition formed about the bridge wire is rendered waterproof by applying a coating of, for example, a lacquer or related waterproofing material. The lacquer usually employed for this purpose is a cellulose derivative lacquer, such as nitrocellulose which generally provides a good waterprooiing protection for the match, thus rendering the match water non-destructible.

Explosives used in marine seismographic prospecting, include an electric initiator, and a main explosive charge which is fired under water. Occasionally, such an explosive accidentally fails to lire or breaks away from the ring line and sinks to the seabed. The initiators presently employed can remain potentially usable under great depths of sea water for long periods of time without desensitization of either the electric match or the detonator explosive. A dangerous situation may thus exist from a misfired charge of a potentially usable initiator being washed up or dragged from the sea.

It has now been found that by coating a water dispersible polymeric material on an electric match for use in an electric initiator having a convenient aperture for the ingress of water, there results a water destructible electric initiator which is useful in the event of misre of the initiator in offshore seismographic prospecting.

In accordance with this invention, an electric match is rendered water destructible with a coating comprising a water dispersible polymeric material. Preferably, the coating comprises polyvinyl alcohol either alone or in combination with wetting agents, limited amount of insolubilizing agents, plasticizers or other additives as desired.

The electric match assembly of the present invention may be prepared as illustrated in the accompanying drawing in which like numerals represent the same elements throughout the several views.

In the ligures:

FIG. 1 is an enlarged half-sectional View taken as a side 3,415,189 Patented Dec. 10, 1968 ICC elevation and illustrating an electric explosion initiator; and

FIG. 2 is an enlarged half-sectional View taken as a side elevation and illustrating an embodiment electric match for use in the initiator in FIG. l.

FIG. 1 illustrates electric explosion initiator 10 having shell 12 in which may be positioned detonating base charge 14 and superimposed thereon, is priming charge 16. The priming charge is normally tired by electric match assembly 18 which may include heat shrunk plastic sleeve 20 for controlling the variation `of ignition time between matches and is thus particllarly useful in seismic detonators. Electric match assembly 18 which is rendered water destructible by addition of an outer coating of a water dispersible polymeric material such as for example, polyvinyl alcohol coating 22, may further include dellagrating composition layer 24, and ignition composition layer 26 forming a core of material about high electric resistance bridge wire 28.

Insulating material base 30 formed of an electric nonconductive material such as, for example, cardboard, is

provided with electric conductive Iplates 32 and 34 generally formed of a metallic material such as copper or aluminum and applied upon opposite sides of insulating material base 30. Lead wires 36 and 38 are connected to the Iupper ends of electric conductive plates 32 and 34 by a suitable solder material 40. Bridge wire 28 may be similarly sec-ured to the lower ends of electric conductive plates 32 and 34.

Bridge wire 28 may be embedded in ignition composition layer 26 which may, for example, include materials such as cuprous acetylide, diazodinitrophenol, lead mononitroresorcinate, mixtures of lead mononitroresorcinate and potassium chlorate, and related materials and mixtures thereof. The ignition composition layer may be applied in the plastic state about the bridge wire and allowed to harden. Deagrating composition layer 24 which may include mixtures such as ammonium picrate and potassium dichromate, or carbon and potassium chlorate may next be applied and also permitted to harden. Thereafter, one or more layers of, for example, polyvinyl alcohol coating 22 may be applied and permitted to dry.

Shell 12 is desirably formed of metallic material such as copper or aluminum and includes aperture 42 to provide an ingress means for water which renders the assembly water destructible. A water dispersible sealing plug, not shown, may be included to seal aperture 42 which on immersion in water resists the ingress of water into shell 12 for a precalculated period of time sufficient to permit the detonator to be fired. Thereafter, the assembly will be destroyed by water which enters shell 12 by aperture 42 and ultimately desensitizes electric match assembly 18 by dispersing polyvinyl alcohol coating 22 with water saturating the layers coated thereby.

Although aperature 42 is illustrated near the bottom of shell 12, it is recognized that the aperture may be positioned at any convenient location on the shell such as about bridge Wire assembly 18 which increases the rate at which the assembly may be destructed by water since less resistance by materials contained within shell 12 is present.

Sealing plug 44 is illustrated at one end of shell 12 for supporting lead wires 36 and 38 coated with a suitable insulating material 46 such as polyvinyl chloride` Sealing plug 44 may be formed of any suitable material such as rubber, neoprene, or other material which is sufficient elastic for insertion into shell 12 during assembly.

FIG. 2 further illustrates electric match assembly 18 of FIG. 1 except that heat shrunk plastic sleeve 20 is removed. The embodiment of FIG. 2 may be employed in an initiator assembly 10 as illustrated in FIG. 1 and is useful in instances where more rapid destruction of the bridge wire assembly is desired. in the embodiment of FIG. 2, water may attack, for example, polyvinyl alcohol coating 22 about the entire area which which is is applied as opposed to the limited area not covered by heat shrunk plastic envelope 20 of FIG l.

The polyvinyl alcohol coating 22 used in the present invention as the water dispersible polymeric material is found to provide not only water destructible properties by simply `being dispersed or dissolved when in contact with water but is also found to possess a hydrophilic nature upon initial contact with the water. This hydrophilic characteristic appears to increase the ability of water contained within the polyvinyl alcohol coating 22 to permeate into deflagrating composition layer 24 and initiating composition layer 26 to thereby render such materials insensitive to initiation by bridge wire 28.

Polyvinyl alcohol films or resin-like materials for use in the present invention may be characterized as a water dispersible polymeric material which is usually obtained by the hydrolysis of polymerized vinyl esters such as polyvinyl acetate. Polyvinyl alcohol may be yprepared in a number of different degrees of polymerization depending largely upon the extent to which the vinyl compound from which it is derived has been polymerized. The more highly polymerized forms of this water dispersible polyvinyl compound are less soluble in water and produce solutions of higher viscosities for equivalent concentrations than the lower polymers. There are also a large number of the so-called partial derivatives of polyvinyl alcohol in which some of the hydroxyl groups in the molecule are replaced by other radicals such as ester radicals or acetal radicals. Such partial derivatives may be produced by the incomplete saponication of vinyl esters or by the incomplete reaction of polyvinyl alcohol with aldehydes or other compounds which react with hydroxyl groups. The properties of the partial derivatives of polyvinyl alcohol vary in accordance with the proportion of hydroxyl radicals that have been substituted by other groups. When the hydroxyl radicals sufficiently predominate, the partial derivatives show essentially the properties of polyvinyl alcohol and are soluble in water as distinguished from the esters, acetals. etc., which are soluble only in organic solvents. Consequently, the term polyvinyl alcohol as used herein designates polyvinyl alcohol and also such partial derivatives thereof as contain a sufhcient number of unsubstituted hydroxyl groups as to render the compound soluble in water.

In coating the match assembly, a suitable solution of polyvinyl alcohol is applied to the surface of the match and the solution is permitted to dry as a suitable solvent such as water evaporates to produce a thin continuous lm surrounding the match head. The concentration of the polyvinyl alcohol solution used for the coating may vary within considerable limits depending `largely on the degree of polymerization of the particular form of polyvinyl alcohol u-sed. In general, aqueous solutions ranging in concentration from about 2% by weight to about 20% by weight of polyvinyl alcohol may be used. However, it has been found that an aqueous solution containing about to about 8% iby weight polyvinyl alcohol is sufficient for use in the present invention and is thus preferred. The polyvinyl alcohol in such instance is that having a viscosity at C. of about 22 to about 224 centistokes.

In some instances, it is advantageous to heat the aqueous polyvinyl alcohol solution to above room temperature in order to decrease its viscosity and to remove any entrained air bubbles which would give rise to the formation of imperfections in the resultant coating. The coating operation may be performed by im-mersionvof the bridge wire assembly into a solution of polyvinyl alcohol which may be at a temperature of about 50 C. Satisfactory coating of polyvinyl alcohol may be obtained at higher or lower temperatures and the solution may be applied in other ways, as for example, by Spraying or by brush application.

It may be found advantageous to incorporate in an aqueous polyvinyl alcohol solution, a surface tension reducing agent. In addition to uniform wetting, such agents also have the advantage of decreasing the tendency for air bubbles to adhere to the surface of the assembly during coating. Any of the common water-soluble wetting and surface tension reducing agents known to the art which do not adversely affect deagrating composition layer 24 and ignition composition layer 26 may be employed. Wetting agents comprising sulfonation products of higher aliphatic alcohols have been found to be particularly useful.

When it is desired to characterize the polyvinyl alcohol coating less sensitive to water destruction, this may be accomplished by using agents which tend to coagulate or insolubilize polyvinyl alcohol. Examples of materials which are suitable for this purpose are various inorganic compounds such as borates, perborates, silicates, chromic acid, chromates, dichromates, alum and ferrie chloride, and organic hardening agents such as tannins, formaldehyde, and other alde-hydes, azo dyes and the like. These insolubilizing agents may be applied as a separate thin layer independent of the polyvinyl alcohol layer or may be applied as part of the polyvinyl alcohol solution although this is not usually desirable for the reason that such materials tend to increase the viscosity of the polyvinyl alcohol solution and render application thereof to the `[bridge wire assembly somewhat difficult. The polyvinyl alcohol film may be rendered suciently water resistant such that the film will not soften under varying humidity conditions.

Although polyvinyl alcohol film is generally elastic and exible and ordinarily does not require the addition of softening agent, plasticizers may be employed to increase the iiexibility of the lm if desired.

The normal method of applying the layers of compositions forming electric match assembly 18 is that of dipping the assembly in a liquid containing the required ingredient for a particular layer being applied. A binding agent may be employed such as, for example, nitrocellulose, and a solvent, for example, a-myl acetate may be employed which is thereafter dried to remove the solvent and to deposit the layer of composition on t-he assembly. The aqueous polyvinyl alcohol solution may be simply air dried or alternately may be dried in warm air at a ternperature such as for example, of about 50 C.

Various additional materials may be employed in place of polyvinyl alcohol coating 22 as the water dispersible polymeric material which may also be -generally characterized as film forming ingredients. Additional materials may include water dispersible cellulose ethers such as methylcellulose, carboxymethylcellulose, hydroxyethylcellulose and the like; other water dispersible polyvinyl compounds such as polyvinylpyr-rolidone, polyvinyl methyl ether, and the like; and water dispersible `alkali rnetal salts of polyacrylic acid `such as the :sodium and potassium salts thereof. Additional water dispersible polymeric material for use 'herein will be readily apparent to those skilled in the art.

Since there is a limit to the thickness of a layer which may be deposited on dipping, it is recognized that in forming the match fusehead, two Ior more dips of each layer of composition may be applied. Moreover, succesive ilayers may include compositions of different physical or chemical ingredients, if desired.

Priming charge 16 is positioned adjacent to base charge 14 and in detonating relation thereto and to deflagrating composition layer 24. The priming charge may include any suitable material such as mannitol hexanitrate, diazodinitrophenol, mercury fulminate, lead azide, or mixtures thereof with oxidizing agents such as potassium chlorate.

Base charge 14 may include any suitable detonable material, for example, pentaerythritol tetranitrate, nitrostarch, trinitrotoluene, teryl or the like.

Deagration composition layer 24 positioned over the ignition composition layer 26 as part of electric match assembly 18 includes any suitable material such as for example, a mixture of carbon and potassium chlorate.

Matches of the present invention may be used with electric explosion initiators of other varieties than that specically described. For example, the present matches may be used with detonators having various charges and auxiliary elements for special application in other devices where electric matches may be employed. The electric explosive initiators may further include delay trains, if desired.

It is understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electric match assembly which comprises, a bridge wire assembly having a bridge wire electrically connected at one end thereof, a match head surrounding said bridge wire, and a water dispersible polymeric material coating layer disposed on and surrounding said match head.

2. The electric match assembly of claim 1 wherein the match head includes an ignition composition layer disposed about the bridge wire and a fdeagrating composition layer disposed about said ignition composition layer.

3. The electric match assembly of claim 1 having a heat shrunk plastic sleeve disposed about a length of the electric match assembly.

4. The electric match assembly of claim 3 in combination with an electric explosion initiator having an outer shell containing an explosive charge and provided with an aperture for the ingress of water into the initiator, said combination for use in seismographic prospecting.

5. The electric match assembly of claim 1 disposed in an electric explosion initiator having an outer shell containing an explosive composition and provided with an aperture for the ingress of water into the initiator.

6. The electric match assembly and electric explosion initiator of claim 5 wherein the aperture for ingress of water into the initiator is disposed near the base of the initiator whereby ingress of water permeates the contained explosive composition prior to contacting the water dispersible polymeric material coating layer disposed on said match head.

7. The electric explosion initiator of claim 5 wherein the contained explosive composition includes a detonating charge and a priming charge in detonating position relative to the electric match assembly.

8. The electric match assembly of claim 1 wherein the water dispersible polymeric material is a water dispersible polyvinyl compound.

9. The electric match assembly of claim 8 wherein the water dispersible polyvinyl compound is polyvinyl alcohol.

10. The electric match assembly of claim 1 wherein the water dispersible polymeric material is a water dispersible alkali metal salt of polyacrylic acid.

11. The electric match assembly of claim 1 wherein the water dispersible polymeric material is a water dispersible cellulose ether.

12. The electric match assembly of claim 1 wherein the water dispersible polymeric material coating layer is a polyvinyl alcohol coating layer applied as an aqueous solution containing from about 2% to about 20% by weight of polyvinyl alcohol, said' solution having a viscosity at 20 C. of about 22 about 24 centistokes.

References Cited UNITED STATES PATENTS 1,935,495 11/1933 Young 102-28 X 3,279,372 10/ 1966 Patterson 102-28 3,322,066 5/1967 Gril-lith et al 102-24 3,332,350 7/1967 Morfy 102-28 3,356,024 12/ 1967 Driscoll et al 102-28 3,358,601 12/1967 Dittmann et al 102-28 BENJAMIN A. BORCHELT, Primary Examiner. VERLIN R. PENDEGRASS, Assistant Examiner. 

